Obtaining accurate and consistent intake and output measurements of fluids is a matter of very high priority in treating critically ill hospital patients. Intake measurements are essential to insure that the prescribed volume and rate of parenteral/interal solutions are delivered so that the desired therapeutic effect occurs. Accurate and consistent output measurements are essential to insure that fluid overload as a result of over infusion, depressed cardiac output, or post-renal failure have not occurred. Acute changes in urine flow can be the earliest evidence, even before changes in the vital signs of blood pressure, temperature, pulse, or respiration of a deteriorating clinical condition in the patient.
For a critically ill patient who does not have primary renal failure, the flow and volume of urine produced by the kidney is dependent upon adequacy of renal blood flow. Since cardiac output is the primary determinant of renal flow, changes in urine output are correlated with changes in cardiac output. Thus, an accurate measurement of the rate of urine flow and volume can supply a physician with information relating to potential circulatory arrest and acute renal failure. A brief episode of only five minutes of hyper-tension to 66 percent of the patient's normal blood pressure may be sufficient to cause an episode of acute renal failure.
In addition, renal system response to intravenous fluid or blood infusion as observed by change in volume of urinary output, can supply a physician with information about the pathological process responsible for low urinary output. The most common etiology of low urinary output is depressed cardiac output caused by too much fluid volume, but other causes include: primary renal failure, heart failure, or post-renal obstruction.
For the critically ill patient, changes in hemodynamic measurements of cardiac output such as arterial blood pressure, central venous pressure, and left atrial pressure are meaningless if these changes are not correlated with changes in the perfusion of major organs such as the kidney. A urine measuring and display system that can supply the physician indirect information about renal perfusion in the form of changes in the urine volume will insure that he has available the necessary physiologic data to make sound clinical decisions.
Available catheterized patient output volume measuring and collection devices are of three principal designs. Older units are flexible bags or semi-rigid clear plastic disposable collection containers with graduations in 25 or 50 milliliter increments up to 2,000 milliliters. A second system typically consists of a 2,000 milliliter clear flexible bag that incorporates a rigid clear plastic 200 milliliter reservoir which is graduated, initially, in 2 milliliter increments. In these latter instruments, urine flows down a drainage tube into the rigid reservoir. Either every 30 minutes, or hourly, a staff member must measure and record the urine output and then empty the urine from the smaller rigid reservoir into the larger flexible bag, so that the measuring cycle can begin again. Such devices lack accuracy, and are dependent upon precise time interval measurement and recording to establish an accurate record of output. They are difficult to read because the containers hang below the bed. Also, additional time is consumed because of having to transfer the urine from the rigid reservoir into the larger container to begin the measurement cycle again.
A third type of urinary drainage monitor electromechanically separates urine output hourly into one of ten compartments in a disposable unit. This system eliminates emptying of urine from a urinary reservoir every 30 minutes of hourly, but it also lacks accuracy. Its graduations are hard to read, and the design makes it difficult to take thirty minute interval output measurements, resulting in the likelihood that nurses might not check the output every eight hours or at a shift change. The unit is also expensive.
The present invention overcomes the disadvantages set forth for previous systems by employing a system composed of a reusable electronic unit which measures urine output volume to within plus or minus 2 milliliter accuracy using ultrasonic technology. It has digital displays of urine output and time for both the present hour and the prior hour.